What a technician actually does
failed high-voltage diode [S1]
high likelihood advanced $265–$527 installed about 60 min
lights up and spins but does not heat runs but the food stays cold
The most frequent no-heat failure and the cheapest part: a one-way electrical valve that either works or does not, so it fails suddenly with no decline beforehand. S2 adds that it works with the capacitor to push the transformer up to roughly 4,000 volts, that a shorted diode often announces itself with a loud buzzing hum and sometimes a tripped breaker, and that it is not a DIY part. S1 deliberately publishes no per-component medians for microwaves because the sample is too small, so the figure here is its overall completed-repair range ($265-527, median $376).
the sources do not publish a per-component figure for microwaves; the cost shown is the overall completed-repair range the source does publish
failed magnetron [S2]
high likelihood advanced $180–$350 installed about 90 min
heats weakly and takes twice as long
The tube that actually produces the microwave energy. It wears out rather than failing outright, so the first sign is everything taking longer: a cup of water that took 90 seconds now takes three minutes. S2 puts an installed magnetron at $180-350, which it notes frequently exceeds the value of a countertop unit. The water test makes this measurable: one cup of cold water on full power for two minutes should come out steaming. S1's replacement line is a failed magnetron on a unit already past ten years. Time basis: no published duration, book estimate.
priced by the source as an installed replacement; no part-only figure is claimed
failed high-voltage capacitor [S2]
medium likelihood advanced $265–$527 installed about 60 min
runs but the food stays cold
Produces no heat and often a humming noise. Both sources are emphatic that this is where the danger sits: the capacitor holds thousands of volts long after the unit is unplugged, sometimes for a long time, and has to be discharged deliberately with a bleeder resistor before anything inside can be touched. Contact can be fatal. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
failed high-voltage transformer [S2]
medium likelihood advanced $265–$527 installed about 75 min
lights up and spins but does not heat
S2's tell is electrical rather than thermal: a failed transformer often trips the breaker or blows the fuse immediately when the cook cycle starts. A loud hum with cold food points at the transformer or a failing capacitor, and both draw heavily as they fail. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
door interlock switches [S1]
medium likelihood advanced $265–$527 installed about 60 min
lights up and spins but does not heat
The safety design that stops the magnetron firing unless the door is properly closed and latched. When a latch hook wears or a switch fails, the control never receives permission to start, so the display and light work and nothing else does. A door that rattles, needs a firm push or has become loose points straight at this. S2 notes the monitor switch can also signal not-closed while the light and fan still run. Cost basis: the source publishes only the overall repair range for microwaves. Time basis: no published duration, book estimate.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
burnt or soiled waveguide cover (arcing) [S1]
medium likelihood advanced $265–$527 installed about 60 min
runs but the food stays cold
The small mica panel on the interior side wall that protects the opening where energy enters the cavity. Once it is soiled or burnt through it arcs, and continued arcing damages the magnetron, turning a small repair into a large one. S1's instruction is to stop using the unit: sparking, a burning smell or scorch marks inside mean unplug it and have it looked at. Cost basis: the source publishes only the overall repair range for microwaves.
no per-component figure is published for microwaves; the cost shown is the overall completed-repair range
Repair or replace?
If you can carry it, replace it. If it is bolted to the wall or built into cabinetry, repair it. A countertop unit's repair approaches the price of a new one that arrives with a full warranty; a built-in or over-the-range unit means matching a cutout or a mounting and dealing with venting, and a discontinued model can turn a swap into cabinetry work. The one exception on a built-in is a failed magnetron past ten years. [S1]
- Typical completed repair: $265–$527 [S1]
- Comparable new unit: $130–$1,000 [S1]
- Planning life used for the decision: 10 years
- The installation decides this one, not the part: roughly $130 for a countertop replacement against a $265-527 repair, $450-850 plus installation over the range, and above $1,000 built in.
the source's replacement line: a failed magnetron on a unit already past ten years is the one case where replacement wins even on a built-in, because the other components are near the end of their life too. Replacement prices by type come from S2: countertop around $130, over-the-range $450-850 plus installation, built-in and drawer units above $1,000
Run your own quote through the calculator — the same half-of-new-price rule with your numbers.
Do this first (free)
demo (showroom) mode left switched on [S1]
high likelihood easy no part needed about 5 min
runs but the food stays cold lights up and spins but does not heat
The one free cause, and the source calls it the single most common no-fault reason a microwave behaves exactly like a broken one: the display lights, the turntable spins, the fan runs, the timer counts down and the magnetron never fires. It exists so retailers can run units on a shop floor, and it gets switched on accidentally by a child pressing a key sequence or by a power event. On most models you hold a specific key (commonly 1, Off or Cancel) for several seconds; the model manual gives the exact sequence. Free.
tripped thermal cutout from restricted airflow [S1]
medium likelihood easy no part needed about 30 min
heats for a minute then stops heating
Heat that works and then cuts out mid-cycle is thermal protection doing its job, not a failed part: the cutout shuts the magnetron down when it exceeds a safe temperature, and on over-the-range units the usual cause is grease filters clogged with cooking residue so the fan cannot move air. Cleaning them is free; replacement filters are inexpensive and neither source prices them. S2 adds the maintenance rule: clean the grease filter monthly and replace the charcoal filter yearly on recirculating installations.